Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $168.88   13.733%   $192.0723   $192.07   $192.05   $192.10  
  Purchase #2 $219.68   11.233%   $244.3567   $244.36   $244.35   $244.40  
  Purchase #3 $122.83   5.177%   $129.1889   $129.19   $129.20   $129.20  
  Purchase #4 $244.38   12.359%   $274.5829   $274.58   $274.60   $274.60  
  Purchase #5 $222.96   8.582%   $242.0944   $242.09   $242.10   $242.10  
  Purchase #6 $76.69   5.462%   $80.8788   $80.88   $80.90   $80.90  
  Purchase #7 $82.68   12.806%   $93.268   $93.27   $93.25   $93.30  
  7 purchase totals = $1,138.10       $1,256.4420   $1,256.44   $1,256.45   $1,256.60